Self‐Powered Smart Textile Based on Dynamic Schottky Diode for Human‐Machine Interactions

Abstract The growing demand for sustained self‐powered devices with multifunctional sensing networks is one of the main challenges for smart textiles, which are the critical elements for the future Internet of Things (IoT) and Point of Care (POC). Here, cellulose‐based smart textile is integrated with dynamic Schottky diode (DSD) to generate sustained power source (current density of 8.9 mA m⁻2) for self‐powered built‐in sensing network. In response to normal and shear motions, a pressure sensor with a sensitivity of 0.12 KPa⁻1 and an impact sensor are demonstrated, respectively. The woven structure of the textile contributes to signal amplification, which can also form a matrix of sensing elements for distributed sensing. The proposed strategy of fabricating self‐powered and multifunctional sensing networks with smart textiles shows tremendous potential for future intelligent society.


Self-powered Smart Textile based on Dynamic Schottky Diode for Human-Machine Interactions
Pengfei Deng, 1 Yanbin Wang, 1 Ruizhe Yang, 2,3 Zijian He, 1 Yuanqiu Tan, 4 Zhihong Chen, 4 Jun Liu, 2,3 * and Tian Li 1 * This PDF file includes: Figure S1. Schematic of mechanism of dynamic Schottky diode Figure S2. Signal output of one-junction organic-metal contact Figure S3. SEM and EDX mapping of composite thread coated with PEDOT: PSS Figure S4. SEM and EDX mapping of nonwoven textile coated with PEDOT: PSS Figure S5. Long-term continues cycling between samples with and without oil-isolation Figure S6. EIS of samples under dry and wet conditions Figure S7. Comparison of moisture content dependent Jsc and Voc EC signals in different pairs Figure S8. Mechanism of EC reaction and hydrophilicity change after decaying Figure S9. Hydrophilicity of textile before decaying Figure S10. Hydrophobicity of textile after decaying Figure S11. Comparison of 4 types of signals outputs in Al-Zn pair Figure S12. Comparison of 4 types of signals outputs in Al-Ni pair Figure S13. EC signals of Zn in pair of polished Al (Al 2 O 3 ) Figure S14. EC signals of Zn in pair of finished Al Figure S15. SEM of textile interface 1 in Al-Al (dry) pair Figure S16. EDX mapping of textile interface 1 in Al-Al (dry) pair Figure S17. EDX spectrum of textile interface 1 in Al-Al (dry) pair Figure S18. SEM of textile interface 2 in Al-Al (dry) pair Figure S19. EDX mapping of textile interface 2 in Al-Al (dry) pair Figure S20. EDX spectrum of textile interface 2 in Al-Al (dry) pair Figure S21. SEM of textile interface 1 in Al-Al (wet) pair Figure S22. EDX mapping of textile interface 1 in Al-Al (wet) pair Figure S23. EDX spectrum of textile interface 1 in Al-Al (wet) pair Figure S24. SEM of textile interface 2 in Al-Al (wet) pair Figure S25. EDX mapping of textile interface 2 in Al-Al (wet) pair Figure S26. EDX spectrum of textile interface 2 in Al-Al (wet) pair Figure S27. SEM of textile interface 1 in Al-Ni (wet) pair Figure S28. EDX mapping of textile interface 1 in Al-Ni (wet) pair Figure S29. EDX spectrum of textile interface 1 in Al-Ni (wet) pair Figure S30. SEM of textile interface 2 in Al-Ni (wet) pair Figure S31. EDX mapping of textile interface 2 in Al-Ni (wet) pair Figure S32. EDX spectrum of textile interface 2 in Al-Ni (wet) pair Figure S33. SEM of textile interface 1 in Al-Zn (wet) pair Figure S34. EDX mapping of textile interface 1 in Al-Zn (wet) pair Figure S35. EDX spectrum of textile interface 1 in Al-Zn (wet) pair Figure S36. SEM of textile interface 2 in Al-Zn (wet) pair Figure S37. EDX mapping of textile interface 2 in Al-Zn (wet) pair Figure S38. EDX spectrum of textile interface 2 in Al-Zn (wet) pair Figure S39. Electrode metal selection Figure S40. Photos of a nonwoven textile device after washing Figure S41. Output of DSD signals after washing

Mechanism of dynamic Schottky diode
The Schottky diode is formed when metal and semiconductors are in physical contact. A metalsemiconductor junction between a metal and p-type semiconductor creates a barrier or depletion layer. Eventually, electron transfer occurs due to the mismatched surface energy levels when reaching a thermodynamic equilibrium after the alignment of Fermi energy levels at two sides.

Transient signal of one-junction organic-metal contact
A multimeter (DAQ6510, Keithley) was used to record the signal outputs. Each weft and wrap wire will form a Schottky diode in a woven structure. When mechanical impact like tapping and friction is applied, the dynamic Schottky diode signals will generate. After the motion disappeared, the output returned to zero baseline.

Figure S2. Signal output of one-junction organic-metal contact SEM and EDX mapping of composite thread, and nonwoven textile
In Figure

Long-term continues cycling between samples with and without oil-isolation
Another lifespan testing with continuous cycling is conducted under 1N pressure with/ without paraffin oil, aiming to measure mechanical loss. After 5500 cyclings, the opencircuit voltage of the device with paraffin oil decreased from -0.08 V to -0.05 V. In contrast, that of the device without paraffin oil decreased from -0.09 V to -0.02 V. Higher final output has shown in device with paraffin oil, even though it has lower initial output. It's found that the existence of paraffin oil decreases mechanical loss, which is in line with our previous assumption.  The PEDOT: PSS aqueous solution/dispersion has an excess amount of PSS to enhance the hydrophobic PEDOT particles in water. The interface absorbs water from the environment, and the excess PSSH in the PEDOT: PSS film dissociates into proton and PSS ions again, making the interface conductive. As the PEDOT core is hydrophobic and surrounding PSS is hydrophilic, the cellulose and PEDOT: PSS complex shows hydrophilic properties overall. However, with the electrochemical reaction of metals and PEDOT: PSS at the interfaces, the surrounding PSSwill combine with metal ions, and PEDOT can be reduced to its neutral state. The first reaction is between protons and the negative electrode, where it consumes negative electrode material. The second reaction is between the negative electrode and PEDOT: PSS [1] : Consequently, the negatively charged PSS ions detach from the PEDOT chains, which will pair with the metal ions released from the negative electrode. The hole density in the PEDOT chain decreases and the hole transfer is retarded, leading to the decay of output signals ( Figure S8). At first, the hydrophilic PSS-rich grain covers the hydrophobic PEDOT-rich grain, making the film appear hydrophilic ( Figure S9    It's well known that the more reactive metal acts as the anode in the primary cell. Although Al is more active than Zn, due to an oxide layer (Al 2 O 3 ) on Al, the Zn will act as an anode compared with less active Al 2 O 3 . Therefore, a positive direction of signals emerges when the collecting electrode is connected to the negative terminal of the multimeter ( Figure S13).

Figure S13. EC signals of Zn in pair of polished Al (Al 2 O 3 )
However, when the finished Al after removing the oxide layer is used as a working electrode, it will be an anode, and negative output will appear ( Figure S14).

in Al-Al (dry) pair
Al is found in interface 1 in Al-Al(dry) pair, which comes from the friction between the working electrode and textile. The materials consumption of the electrode here is identified as mechanical loss ( Figure S15-S17). Less Al is found in interface 2 due to the less relative displacement between the collecting electrode and textile ( Figure S18-S20).

in Al-Al (wet) pair
Al is found in both interfaces 1 & 2 in the Al-Al (wet) pair, which comes from the EC reaction and the generation of Al 3+ between the working electrode and textile. The Al 3+ can move in water within the textile, thus leading to its existence in interface 2. Compared to Al-Al (dry) pair, the Al consumption is significantly greater, revealing a dominant consumption of EC reactions. Like the Al-Al (wet) pair, Al in the working electrode serves as the anode; thus, Ni is protected.
Al is significantly found in both interfaces 1 & 2 in the Al-Ni (wet) pair, which comes from the EC reaction and the generation of Al 3+ between the collecting electrode and textile. The Al 3+ can move in water within the textile, thus leading to its existence in interface 2. Due to the larger differences between the two electrodes, the EC reactions will be more intensive. As a consequence, the Al is found to be consumed more than in Al-Al (wet) pair. Compared to the Al-Ni (wet) pair, Zn is significantly found in both interfaces 1 & 2 in the Al-Zn (wet) pair, which comes from the EC reaction and the generation of Zn 2+ between collecting electrode and textile. The Zn 2+ can move in water within the textile, thus leading to its existence in interface 1. Meanwhile, the Al will be protected by the Zn electrode while Zn works as an anode here, accounting that Al is found to be less than that in Al-Al (wet) pair. This phenomenon is in line with the previous direction of the Al-Zn pair. shown in Figure S39 that the Al-Al pair has the largest output compared with the other two, specifically in the case that PEDOT; PSS works as the organic semiconductor.

Washability test
To test the washing durability of the textile device, we stirred our samples in beakers at 600 rpm for 1h to imitate the laundry washing for each cycle. The samples are prewashed for 30 min before the washing cycle to remove the materials that are deposited on the surface of the textile.
All the samples have been washed for 3h in total. After each cycle, the sample was air-forced dried in an oven at 100 °C and annealed on the hot plate at 100 °C for 15 min. After drying, the DC outputs are measured. Photos of samples after each cycle are shown in Figure S40. Partial PEDOT: PSS on the surface has been washed away after several hours, as the textile turns white in some areas. However, most PEDOT: PSS still adhered to the cotton threads even after 3h wash due to the bonding between PEDOT: PSS and textile. The DC outputs after each cycle are shown in Figure S41. washing, the output still shows the level of 0.2 V as most PEDOT: PSS still bonds with the textile and is capable of forming Dynamic Schottky Diode. For further enhancement of washability, superhydrophobic treatment such as fluoroalkyl silane [2] , fluorinated polymer sponge [3,4] , or surface encapsulation such as silicone [5] and rubber [6] sealing can be applied.